FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Article Id 194332
There are some rare cases where the power LED is seen to be blinking red.  This is not documented in the hardware manuals.

This may mean that the device is having a hardware failure.  Shown symptoms may include the device hanging but that it functions normally again after a reboot.

If the symptoms are seen multiple times it is recommended to open a support ticket to request troubleshooting and potentially a RMA exchange.